An electronic amplifier is a device for increasing the power of a signal. It does this by taking power from a power supply and shaping the output to match the (relatively low power) input signal. This process invariably introduces some noise and distortion into the signal, and the process cannot be 100% efficient – amplifiers will always produce some waste heat. An idealized amplifier can be said to be “a piece of wire with gain“, as the output is an exact replica of the input, but larger.

Different designs of amplifier are used for different types of applications and signals. We can broadly divide amplifiers into three categories – small signal amplifiers, low frequency power amplifiers and RF (radio frequency) power amplifiers. Each of these calls for a slightly different design approach, mainly because of the physical limitations of the components used to implement the amplifier, and the efficiencies that can be realized.